I'm running v4 and v5 right now and both have had this problem on different occassions. Whenever I login, it will give me an error (HTTP status 400 - Invalid direct reference to form login page). When I backspace, it logs me into the app. HOwever, whenever I click on anything, it prompts me to login every time. I've rebooted in the past and it clears up but this isn't always an option. Any idea what is happening?